FIELD OF THE INVENTION
The invention generally relates to the development of cold helium gas transfer device for a 200kW HTS motor. More particularly, the present invention relates to a cold helium gas transfer device for (HTS) motors to improve inflow of helium gas between rotating part of the motor and a stationary supply source of cold helium gas.
BACKGROUND OF THE INVENTION
Transfer coupling is a device which enables transfer of cold helium gas between rotating members, such as pole coil housing of a superconducting rotor and non-rotating member of a refrigerating machine.
Accordingly, the present invention provides a rotating helium transfer coupling device with housing chamber and bellow seal assembly which gives leak rate of the order 10 ^-6 mbar litres per sec.

The device of the present invention is a unique and less intricate construction for HTS motor with metallic bellow seal and grafoil packing arrangement.
Prior published patents on cooling of superconducting motor such as
US 6812601, US 4056745, US 775989, US 3845639, all discloses unique cooling arrangements. They have different constructions with various types of seals such as Ferro fluid seals, graphite seals, carbon face seals, bellow seals etc. Their construction involves cryogenic rotating seals and couplings, adjustable throttle valves etc. These arrangements comprise compound and complex components.
In rotating electrical machines having superconducting windings, devices for the transfer of helium gas typically have to be able to inject helium gas into a cryostat containing a superconducting winding to cool the winding. The devices also have to be able to extract the gaseous helium from the cryostat after the helium gas gets heated from being in contact with the superconducting winding. Finally, the devices are used to return the gaseous helium to the refrigerating machine to cool the helium gas again at the required low temperature.

OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a cold helium gas transfer device for high temperature superconducting (HTS) motors to improve inflow of helium gas between rotating part of the motor and a stationary supply source of cold helium gas.
Another object of the invention is to propose a cold helium gas transfer device for high temperature superconducting (HTS) motors to improve inflow and outflow of helium gas between rotating part of the motor and a stationary supply source of cold helium gas, wherein the cold helium gas transfer device comprises metallic bellow seal and grafoil packing arrangement.
A still another object of the invention is to propose a cold helium gas transfer device for high temperature superconducting (HTS) motors to improve inflow and outflow of helium gas between rotating part of the motor and a stationary supply source of cold helium gas, wherein the HTS motor at one embodiment is of 200 kW capacity and the mass flow rate of helium gas required to cool the rotor of the motor is 1.5 grams per sec.

A further object of the invention is to propose to propose a cold helium gas transfer device for high temperature superconducting (HTS) motors to improve inflow and outflow of helium gas between rotating part of the motor and a stationary supply source of cold helium gas which provides a limited leak rate of 10^-6 mbar liters per second.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a rotating helium transfer coupling device with housing chamber and bellow seal assembly which gives leak rate of the order 10^-6 mbar liters per sec.
The device of the present invention is a unique and less intricate construction for (HTS) motor with metallic bellow seal and grafoil packing arrangement.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING
Figure 1 shows cross sectional view of helium gas transfer device according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION
The windings of a superconducting rotor are cooled by cold helium gas at 25K using a helium transfer coupling device. Usage of cryogenic coolant such as helium has substantial benefits in cooling superconducting field winding upto 20/25K and having a very low boiling point. Cold helium gas is supplied from an external source through a stationary inlet pipe (11) to the coupling device. In figure 1, the arrows indicate the direction of flow of helium gas. Helium gas is pumped into the rotor from external refrigerating machines through an inlet pipe (11)and warm gas returned from the rotor gets collected in a warm gas collector (7) of a collection chamber (10), and flows through a conduit (13) and finally a low temperature refrigerating machine.
Figure 1 shows cross sectional view of helium gas transfer device of the present invention. All the components of the coupling are mounted on rotating sleeve (1) which is further connected to the housing (3) containing superconducting windings. Other end of the device is connected to the stationary source of refrigerating machine. The device comprises a detachable housing (3) and a

chamber (10) with a warm gas collector (7). A metallic Bellow seal system (6) allows separation of cold inflow helium gas from the refrigerating machine and outflow of warm gas after cooling the rotor windings. Two bearings (5) are mounted on the rotating sleeve (1) with two stopper plates (2). A spacer (4) holds the bearings (5) in position. Inward flow of helium gas takes place through the inlet pipe (11). Outflow of warm gas is collected in the warm gas collector (7) and sent back to the low temperature refrigerating machine through an outlet pipe (13). A metallic bush (8) is inserted over the pipe (11) to prevent any back flow of the cold helium gas, where the bush (8) supported by an inside sleeve (9). 0-rings (14) are inserted in the grooves of inner surface of the rotating sleeve (1) to prevent any back flow of warm helium gas into the rotor.
The test results shows a leak rate of the order 10^-6 mbar liters per sec where the mass flow rate of helium gas required to cool the rotor for 200 KW (HTS) motor is 1.5 grams per sec.

WE CLAIM:
1. A cold helium gas transfer device for high temperature superconducting
(HTS) motors to improve inflow and outflow of helium gas between rotating part of the motor and a stationary supply source of cold helium gas, the stationary supply source supplying through a stationary inlet pipe (11) cold helium gas to the windings of the rotor of the (HTS), a gas collector (7) collecting warm gas returned from the rotor and transferring the gas to refrigerating machine, the device comprising: :
- a detachable housing (3) accommodating the superconducting windings;
- a rotating sleeve (1) mounted with two bearings (5) and two stopper plates (2), and a spacer (4) maintaining the bearings (5) in a position to allow inflow of cold helium gas through the inlet pipe (11);
- a collection chamber (10) comprising a gas collector (7) to collect the warm gas out flowing from the rotor windings; and
- an outlet pipe (13) allowing the warm gas from the collection chamber (10) to flow to the refrigerating machine.

2. The device as claimed in claim 1, wherein a metallic bush (8) is inserted over the inlet pipe (11) to prevent backflow of cold helium gas.
3. The device as claimed in claim 1 or claim 2, wherein the metallic bush (8) is supported inside a stationary sleeve (9) and wherein a plurality of non-metallic '0' rings (14) is inserted in the grooves constructed along the inner surface of the rotating sleeve (1).
4. The device as claimed in claim 1, comprising a metallic bellow seal arrangement (6) which allows separation of inflow of cold helium gas and outflow of warm gas after cooling the rotor windings.